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<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>
  <p>收到a页面的值：<span id="data"></span></p>
  <script>
    var data = 'bbbbbbb'
    window.addEventListener('message', function(msg) {
      document.getElementById('data').innerText = msg.data
      var timer = setTimeout(function() {
        window.parent.postMessage(data, 'http://www.cross.com:3000')
        clearTimeout(timer)
      }, 1000)
    })
  </script>
</body>
</html>